Diving Medicine

By Dr. David Sawatzky

Every diver knows that when they go diving they need to pee. They also know that any cold water diver who claims never to have peed in their wetsuit is either lying or has logged very few dives. Finally, it’s fair say that virtually all advanced divers use drysuits and those of us who routinely make dives of three to six hours duration must have figured out how to get around this problem.

Water constitutes 40 to 75 percent of the body’s weight, a wide range due to individual fat content and its percentage of overall weight. Skeletal muscle is over 75 percent water; skin is over 70 percent; heart, lungs and kidneys are 80 percent. Fat is only 10 percent water. Therefore, water amounts to a much smaller percentage of total body weight in grossly obese people. In general, body weight of normal young adult males is 60 to 70 percent water while normal young adult females are at 50 to 60 percent. On average, women have a higher percentage of body fat than men.

The amount of water in the body must be maintained within a fairly narrow range. We get water from three main sources. Daily food provides about 1,000 ml, drink about 1,200 ml and metabolism produces another 350 ml. When food is metabolized the main waste products are water and carbon dioxide. On a regular cycle we lose water as urine (1,500 ml), feces (100 ml), through the skin (600 ml) and lungs (350 ml). The lungs always saturate the air with water before it gets to the alveoli and therefore, if we are breathing dry air (diving) more water is required to humidify the gas. When our output of water is increased, our intake must also increase to prevent dehydration. During extreme exercise in a hot environment, intake might have to exceed four gallons (15 liters) a day to maintain balance!

Some urine production is inevitable. When we eat and digest protein, nitrogen is produced as a waste product and we eliminate it as urea in our urine. Our kidneys can only concentrate urine to a limited degree and some water is lost diluting the urea so that we can pee it out. However, if our urine is chronically concentrated we run the risk of forming kidney stones. No one wants to experience the pain of passing a kidney stone so we should always drink enough water to keep our urine dilute.

Peeing and Gravity

Why do we produce more urine when we go diving?

When we enter the water, we take away the effect of gravity. Gravity normally causes a fair amount of blood to stay in our legs and arms. When we are in water, this blood moves back into the chest area. Our bodies sense this increase in blood volume in the chest and interpret it as too much blood/water. It sends a signal to our kidneys to get rid of this excess water. Therefore our kidneys produce more urine and we have to pee. When we get out of the water after swimming or diving, gravity reasserts its pull and blood pools in our arms and legs. As a result the body senses less blood/water in the chest and sends a signal to the kidneys to conserve water.

A second reason we need to pee when we dive results from the cold. If we become cold, our bodies attempt to conserve heat by allowing the arms and legs to become colder. We move blood from our arms and legs and keep it in the stomach, chest and head to keep the vital organs in these areas warm and functioning properly. Again, our bodies sense this extra blood in the chest and send a signal to our kidneys to produce more urine to eliminate this excess water. When we warm up after the dive we will again be relatively dehydrated.

Informed, Uninformed

Many divers know that they will be cold during a dive and so consume hot drinks beforehand in an attempt to stay warmer while underwater. This extra fluid will be eliminated during the dive, resulting in the need to pee. More informed divers consume stimulants like the methyl xanthenes (caffeine) in chocolate, cola, tea and coffee before a dive. They know these chemicals increase the basic metabolic rate of the body and result in more heat production. They will be warmer during the dive but the chemicals in these drinks typically result in the production of more urine than the amount of water that was contained in the drink! Once again, there is the urge or need to pee during the dive.

Completely uninformed divers will drink alcohol before diving. As anyone who’s consumed alcohol knows, this results in increased production of urine. If the alcohol was consumed close to the time of the dive, the increased production of urine will occur during the dive.

These are the primary reasons we have to pee when we go diving.

Problem Solving

There are several ways in which divers attempt to deal with this problem. Some intentionally become dehydrated before they go diving. This will be effective in reducing the amount of urine produced during the dive, but it is a very bad idea. Dehydration is a major risk factor for decompression sickness. There are many other reasons why divers are dehydrated during/after every dive so it is good practice to consume hydrating fluids before and after diving.

Some divers just pee in their wetsuits. This has the added benefit of making you feel a bit warmer during the dive. Remember to rinse your wetsuit out thoroughly after the dive and periodically wash it with detergent. Peeing in a drysuit is just not a good idea. Not only is it messy, it will degrade the effectiveness of your underwear and you will become extremely cold.

Fortunately, there are several options available to drysuit divers. Don’t knock adult diapers until you’ve given them a try. They will contain the urine (and if necessary other waste products), keep your thermal underwear dry, warm (clean) and they’re also relatively easy to deal with after the dive. It’s been my experience using diapers that they help keep the crotch area warm, often eliminating the need to pee.

For years male technical divers have had pee valves installed in their drysuits. Basically you wear a condom catheter and attach the catheter to the inside of the pee valve when you put on the drysuit. If you have ever wondered why some guys appear to be playing with themselves as they don their drysuits, you now know what they (most likely) were doing. During the dive, when the need to pee arises the diver opens the pee valve, pees into the water, and closes it again.

I tried this technique when I first started technical diving but there are several problems. Wearing a condom glued to your penis for several hours is not particularly comfortable. If the catheter slips off the pee valve you will pee into your drysuit (not uncommon). If the condom comes off during the dive or is not ‘pee tight’ you have the same result, as with a kink in the catheter. If the catheter/condom comes off, water will enter the drysuit when you open the pee valve. If the pee valve leaks you also get wet. Finally, condom catheters are use-and-throwaway and the cost does add up.

Female tech divers have similar options. They can use diapers. They can use the female equivalent of a condom catheter and pee valve (see www.she-p.com). This silicone device glues to the skin and has a tube that attaches to a pee valve. I do not know any female divers who have tried this device but it likely has shortcomings similar to the condom catheter.

Both sexes could catheterize themselves and wear a bag under the drysuit or connect the tube to a pee valve. This is a better option for females since the urethra (tube from the outside to the bladder) is very short and catheterization is normally a simple procedure. It’s more complex and uncomfortable for males.

Anti-Pee Pill

In my opinion there is a better solution for both sexes. The body signals the kidneys to produce more or less urine via the antidiuretic hormone (ADH); natriuretic peptides and the renin-angiotensin-aldosterone system primarily control electrolyte excretion. As the level of ADH decreases the kidneys produce more urine. As I’ve explained, the production of urine is increased during most dives due to immersion and cold, resulting in dehydration after the dive and increasing the risk of DCS.

In 1998 a tech diving friend mentioned that some racecar drivers took a chemical to avoid having to pee when racing and he wondered if this would be safe to use while diving. I investigated and found that they were taking desmopressin acetate. This chemical is readily available because it is commonly used to treat bed-wetting in kids. Taken before bed it helps youngsters reduce urine production so nighttime peeing is unnecessary. In fact, desmopressin acetate is a synthetic structural analogue of ADH. This struck me as a perfect solution. Not only would it eliminate the problem of having to pee during a dive, it should counteract the production of urine due to immersion and cold, and it should reduce the risk of DCS. I got a friend to write me a prescription (sold in Canada as DDAVP) and gave it a try.

DDAVP comes in several forms (nasal spray, sublingual tablet and tablets you swallow). I swallow a 0.1 mg tablet about an hour before diving (it takes about an hour to become effective) and have found that it works all day (references suggest it lasts six to 12 hours). Urine production is reduced but not eliminated. After six or seven hours in a drysuit I can go for a pee at my leisure and then do another six to seven hours in the drysuit without difficulty. Children over age five can take up to

0.6 mg of this chemical every night so, comparatively, I’m using a very small dose. At this dose there is virtually no downside. At higher doses, if the person also consumes large quantities of water they can upset the electrolyte balance in the body. Also at higher doses, when the drug wears off a significant quantity of urine can be produced to restore fluid balance. I have been using DDAVP before long dives for 12 years now and still believe it to be the best option. Cost is about $2 per pill in Canada and twice that in the USA.

7 Responses to “Why Do I Need to Pee Every Time I Dive?”

Thanks for writing this article — it’s very interesting and I know divers ask this question a lot.

I have a comment about one part in particular though:

“When we enter the water, we take away the effect of gravity. Gravity normally causes a fair amount of blood to stay in our legs and arms. When we are in water, this blood moves back into the chest area. Our bodies sense this increase in blood volume in the chest and interpret it as too much blood/water. It sends a signal to our kidneys to get rid of this excess water. Therefore our kidneys produce more urine and we have to pee. When we get out of the water after swimming or diving, gravity reasserts its pull and blood pools in our arms and legs. As a result the body senses less blood/water in the chest and sends a signal to the kidneys to conserve water.”

I don’t believe this is the case. Gravity acts on our bodies at depth just as it does on the surface. The only difference being that there’s a buoyant force pushing us up against gravity when we’re in the water. When this upward force equals the downward force due to gravity, we’re neutrally buoyant. Put another way, blood won’t pool in different parts of the body due to a perceived lack of gravity underwater just as crews don’t float around inside submarines at depth.

Blood does tend to pool in the chest area for astronauts in space, even to the point where some have experienced torso and face swelling. This triggers the situation that you explain — the body interprets this as too much fluid, prompting the kidneys to get rid of it. But being weightless in space isn’t the same thing as being neutrally buoyant at depth.

Some researchers have conducted long-term bed-rest studies to simulate some of the physiological aspects of being in space. This got me thinking that maybe spending an extended period in a horizontal position, such as during a bed-rest study or a dive, redistributes fluid in the body enough to trigger the urge to urinate. But if that were the case, very few of us would be getting a decent night’s sleep, so I guess that’s not the reason either.

I’ve talked this over with some dive buddies, and other theories that I’ve heard include dive weights pushing up against their bladder and the fact that they’re surrounded by water during the dive (which might be enough of a trigger on it’s own). For me, I’m definitely guilty of having a little too much pre-dive coffee.

But regardless of these other potential causes, I’m pretty sure that gravity, or a perceived lack of it underwater, isn’t why we need to pee when we dive. I’d be interested to hear your thoughts, especially if I’m missing something about the physics.

This is about one of the most dangerous things I’ve read about. In Britain these drugs are prescription only and that is for a very good reason.You will interfere with post pituitary gland function. At any one time 25% + of blood flow is through the kidneys.Blood pressure is directly affected.Possible side affects:
1)Fluid retention and hyponatraemia(low sodium)
2)In severe cases convulsions
3)If no restriction in fluid intake,stomache pains,headache,nausea,vomiting,allergic reractions,emotional disturbances
4) Nasal sprays can lead to nose bleeds,congestion and inflammation.
The amount of drug is very small measured in micrograms so you can rest assured they are potent
Reference
Britsih National Formulary Sept 2011 page 476
If you think you will go down this road I would not be going in the water with you on any dive let alone one to depth and on mix. Catheters are reversible,this stuff ain’t quite as easy.
YOU HAVE BEEN WARNED
Meeko

This is sort of amusing – one doctor lecturing another on the dangers of a low dose of a drug that’s apparently been around for quite a while and is commonly prescribed to children. I wonder if Dr. Meek is aware that Dr Sawatzky is a dive medicine specialist? At least it appears that he is based on a cursory perusal of literature easily accessed online.

It’s also interesting that in scolding Dr Sawatsky, Dr Meek see fit to remind him that this is a prescription drug. This is interesting primarily because in his article Dr Sawatsky clearly pointed out he had to get a prescription for the drug. Perhaps Dr Meek needs to re-read the article a little more closely?

As a diver who’s both felt and scummed to the inevitable urge, I’d personally be pretty interested in learning more about this drug. Given the obvious benefits of reducing dehydration (and I do hope that Dr Meek understands the relationship between dehydration and DCS), I would think more divers should be talking about this drug with their own personal physicians. I can tell you I plan to talk to mine. Given the sporadic dive schedule most divers I know have (we don’t get to dive nearly as often as we’d like, and many folks only get a few trips a year), I’d think a low dose of a drug like this taken only on days you’re going to dive would be a really attractive thing.

Don’t worry, Doc. Meeko may not want to dive with you, but I’m sure there are lots of others out there (myself included) who’d jump at the chance.

Are we sure that dr.sawatzky is a doctor of medicine and not in some other subject as he clearly states that his friend wrote him the prescripton for the drug? If he was a md he could have done that for him self!
I can assure you that many things can affect continance such as middle/old age, prostate problems, childbirth, Resulting in a lot of people that wear diapers in their normal life, , so is it such a big deal to occasionaly don diapers at deapth? Think of it as extra insulation, all medicines have side effects even though you may not esperience them , why risk?

Thanks for writing this! I’m a fairly new diver, and have been wondering whether this is something I should be embarrassed about or not. As a medical professional, I don’t have a lot of qualms about contact with healthy urine, but it’s good to know what is and isn’t normal. And Diana, it may interest you to know that most physicians will not prescribe themselves medication. Self-treatment if typically considered unethical due to lack of objectivity, and is in many places illegal!

I think you have all missed the biggest point and that is cold itself. Cold acts as a vaso constrictor reducing blood flow to the extremities, this reduced blood flow causes blood pressure to increase within your core with the result that your body produces more urine to reduce it. Divers seldom need to pee immediately, instead it is usually after prolonged exposure to cold. This is the sme reason we need to pee when we have been out in the cold walking got example. Gravity has little to do with it, although hydrostatic pressure will have a effect to a degree.